1. Field of the Invention
The present invention relates to a dummy write method for recovering a magnetic head from a write instability state and a drive unit for carrying out the method.
2. Description of Related Art
Metal-in-gap (MIG) heads, thin-film heads, magnetoresistive (MR) heads, giant magnetoresistive (GMR) heads, etc., are known as magnetic heads for hard-disk drive units. In these MIG heads, thin-film heads, MR heads, and GMR heads, particularly in MR and GMR heads, when the head is divided into a head for reading out data and servo information from a magnetic disk, a recording head, and a reproducing head, it is widely known that a write instability phenomenon, in which a read waveform produced by write operation deforms, appears in the reproducing head. Since the state of the magnetic head depends upon the write operation, there are cases where the state becomes better or becomes worse for each write operation.
FIG. 4 shows a characteristic read waveform example of write instability. In the figure, the large amplitude portion in the upper waveform represents a waveform when a servo pattern is read out for obtaining a position error signal (PES) that is used in tracking, and that portion is shown on an enlarged scale on the lower side of FIG. 4. In the example shown in FIG. 4, as evident in the lower waveform, there is shown write instability in which the waveform is offset toward the upper side and is not vertically symmetrical.
There are cases where the magnetic head recovers from this write instability immediately after the occurrence without any write operation, but there are cases where the phenomenon remains. Because of this phenomenon, servo information cannot be read out correctly and a write error will occur. In the worst case, the magnetic head cannot follow a target track and an error will occur in a seek operation. For this reason, a dummy write method has been employed as a method of returning the magnetic head from the write instability state to the normal state.
The present invention is applied to a dummy write method for recovering a magnetic head from a write instability state. This dummy write is performed by performing write operation with a thermally excited, i.e., heated, magnetic head. With this technique, the magnetic head can be restored to write stability more reliably from write instability, compared with the case where it is recovered by the use of a dummy write alone. The present invention is also applied to a drive unit for carrying out the above-mentioned dummy write method.
In one preferred embodiment of a method according to the invention once the write instability has been detected the magnetic head is heated by friction between the magnetic disk and the magnetic head. In this embodiment the dummy write is performed at a landing zone where the magnetic head is parked during non-operation. In still another preferred embodiment, the magnetic head is thermally excited by applying heat to the magnetic head from the outside. A heater is provided at a ramp of a loading/unloading mechanism for lifting the magnetic head during non-operation or in a lift mechanism. A dummy write is performed while the magnetic head is parked on the ramp or lift mechanism and after being heated. Furthermore, in this embodiment, it is preferable that dummy write be performed using a DC erase signal.
The dummy write method employs the fact that the write instability phenomenon varies its state when write operations are performed. The magnetic head performs write operations a few times, using a safe area on or away from the magnetic disk. When the state of the magnetic head improves, i.e., the write instability is removed, and the head cools, a seek operation is performed to the target track and the original normal write or read operation is continued. The dummy write method is performed either in a track following state or when the magnetic head is removed (unloaded) from the magnetic disk.